JP2002090337A - Solid electrolyte type nitrogen oxide gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolyte type nitrogen oxide gas sensor with long-tem stability and its measuring method allowing accurate measurement in a low concentration area in measurement of nitrogen oxide gas concentration in a gas to be measured by means of the nitrogen oxide gas sensor. SOLUTION: In this solid electrolyte type nitrogen oxide gas sensor, a detection electrode layer containing an electronic conductive material, metal nitrate and/or metal nitrite and a counter electrode layer containing the electron conductive material and having a surface covered with a coating material are formed on the surface of a solid electrolyte layer, and a variable potential device and an ammeter are arranged between the detection electrode layer and the counter electrode layer. When voltage is impressed between the detection electrode layer and the counter electrode layer so that the detection electrode layer is set on the positive potential side in comparison with the counter electrode layer or a reference electrode layer, a current value of the electric current flowing between the both electrode layers is measured for measuring a nitrogen oxide gas concentration in the measured gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a gas sensor for measuring a nitrogen oxide gas concentration in an atmosphere and a method for measuring a nitrogen oxide gas concentration using the same. More specifically, the present invention relates to a solid electrolyte type nitrogen oxide gas sensor that exhibits high sensitivity even in a low concentration atmosphere and can stably measure for a long period of time, and the above-described method using the same.

[0002]

2. Description of the Related Art In recent years, there has been an increasing interest in environmental issues, and a gas sensor for measuring and controlling the concentration of nitrogen oxide gas released into the atmosphere has attracted attention. Among such gas sensors, a solid electrolyte type nitrogen oxide gas sensor utilizing changes in the electromotive force or current value of the solid electrolyte is small, simple, and inexpensive, and therefore, its practical application is eagerly desired.

At present, as a method of detecting a nitrogen oxide gas concentration by a solid electrolyte type nitrogen oxide gas sensor which is being considered for practical use, an electromotive force detection method, a current detection method, and the like are known.

A solid electrolyte type nitrogen oxide gas sensor of an electromotive force detection type includes a solid electrolyte layer which is an ionic conductor, a detection electrode layer containing an electron conductive material and a metal nitrate and / or a metal nitrite, and an electron conductive material. It generally comprises a counter electrode layer, a heater for heating these, and a voltmeter provided between the detection layer and the counter electrode layer.
This sensor normally operates by heating a heater to a constant temperature of 100 to 600 ° C. When left in an atmosphere containing a nitrogen oxide gas, the sensor intervenes between the sensing electrode layer and the counter electrode layer via the solid electrolyte layer. Then, a certain electromotive force corresponding to the nitrogen oxide gas concentration is generated. When the concentration of the nitrogen oxide gas in the standing atmosphere changes, the dissociation equilibrium reaction between the metal nitrate and / or metal nitrite and the nitrogen oxide gas contained in the detection electrode layer progresses until the equilibrium is reached, and the detection electrode A change occurs in the mobile ion concentration of the solid electrolyte layer near the layer.

Since this concentration change appears as a change in the electromotive force, the electromotive force at that time is measured with a voltmeter, and a calibration curve showing the correlation between the electromotive force and the nitrogen oxide gas concentration prepared in advance should be used. Can be used to determine the nitrogen oxide gas concentration.

A current detection type solid electrolyte type nitrogen oxide gas sensor comprises a solid electrolyte layer which is an ionic conductor, a detection electrode layer containing an electron conductive material, and an electron conductive material and an alkali metal nitrate and / or an alkali metal nitrite. Including the counter electrode layer,
It generally comprises a heater for heating them, a potential variable device provided between the detection layer and the counter electrode layer, and an ammeter. In addition, in order to stably maintain the potential of the detection electrode layer, in the above-described sensor, the solid electrolyte layer is further provided with a reference electrode layer including an electron conductive material and having a surface coated with a coating material.

[0007] These sensors usually have a heater of 100
Heating is performed to a constant temperature of ~ 600 ° C, and a voltage is applied between the detection electrode layer and the counter electrode layer so that the detection electrode has a negative potential with respect to the counter electrode layer. Then, the mobile ions in the solid electrolyte move toward the detection electrode layer, and the alkali metal nitrate and / or alkali metal nitrite contained in the counter electrode layer dissociates, so that the alkali metal ions similarly move toward the detection electrode layer. And reacts with the nitrogen oxide gas in the gas to be measured in the detection electrode layer to generate alkali metal nitrate and / or alkali metal nitrite. For example, if the nitrogen oxide gas contained in the gas to be measured is nitrogen dioxide gas and sodium nitrite is contained in the counter electrode layer,
In the counter electrode layer, a reaction of NaNO ₂ → Na ⁺ + NO ₂ + e ⁻ occurs, and in the detection electrode layer, the reverse reaction, ie, a reaction of Na ⁺ + NO ₂ + e ⁻ → NaNO ₂ occurs.

As a result, between the sensing electrode layer and the counter electrode layer,
A current value is generated according to the concentration of the nitrogen oxide gas in the gas to be measured flowing from the counter electrode layer toward the detection electrode layer. When the concentration of the nitrogen oxide gas in the gas to be measured that has been left is changed, the current value changes. This current value is measured with an ammeter, and the concentration of the nitrogen oxide gas in the gas to be measured is known by associating the current value with a calibration curve that shows the correlation between the current value and the nitrogen oxide gas concentration. I can do it.

[0009]

The solid electrolyte type nitrogen oxide gas sensor having the above-described structure has the advantage of being small and inexpensive to manufacture, and is therefore accepted as a highly versatile sensor. However, in the case of the electromotive force detection method, there is a problem that the measurement in the low concentration region, which is the most important measurement concentration region for measuring and controlling the nitrogen oxide concentration, is not exactly one step right now. Further, in the case of the conventional current detection method, although the sensitivity in the low concentration range is superior to that of the electromotive force detection method, the alkali metal nitrate and / or the alkali metal contained in the counter electrode layer as the measurement is prolonged. There has been a problem that metal nitrite is greatly consumed and its long-term stability is poor.

[0010] These problems hinder the practical use of solid oxide nitrogen oxide gas sensors. Therefore, it has been desired to develop a nitrogen oxide gas sensor that is accurate in a low concentration region and has excellent long-term stability.

[0011]

Means for Solving the Problems Accordingly, the present inventors have:
As a result of repeated studies to develop a solid electrolyte type nitrogen oxide gas sensor having the above characteristics, a new structure in which the sensing electrode layer formed on the surface of the solid electrolyte layer contains metal nitrate and / or metal nitrite The inventors have found that the above problems can be solved by a gas sensor, and have completed the present invention.

That is, the present invention provides a detection electrode layer containing an electron conductive substance and a metal nitrate and / or a metal nitrite on the surface of a solid electrolyte layer, and a counter electrode having a surface covered with a coating material containing an electron conductive substance. The solid electrolyte type nitrogen oxide gas sensor is characterized in that a layer is formed and a potential variable device and an ammeter are provided between the detection electrode layer and the counter electrode layer.

According to another aspect of the present invention, a voltage is applied between the detection electrode layer and the counter electrode layer so that the detection electrode layer has a more positive potential than the counter electrode layer, using the solid electrolyte type nitrogen oxide gas sensor.
This is a method for measuring the concentration of nitrogen oxide gas, comprising measuring the value of current flowing between both electrode layers and measuring the concentration of nitrogen oxide gas in the gas to be measured.

Further, the present invention provides a method for manufacturing a semiconductor device comprising the steps of:
A detection electrode layer containing an electron conductive material and a metal nitrate and / or a metal nitrite, a counter electrode layer having a surface covered with a coating material containing an electron conductive material, and a reference electrode layer containing an electron conductive material are formed. A solid electrolyte type nitrogen oxide, wherein a potential variable device is provided between the sensing electrode layer, the counter electrode layer and the reference electrode layer, and an ammeter is provided between the sensing electrode layer and the counter electrode layer. An object gas sensor is also provided.

Further, as another invention, the solid electrolyte type nitrogen oxide gas sensor is used, and a voltage is applied between the detection electrode layer and the reference electrode layer so that the detection electrode layer has a more positive potential than the reference electrode layer. And measuring a current value flowing between the detection electrode layer and the counter electrode layer to measure a nitrogen oxide gas concentration in the gas to be measured. .

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The gas to be measured by the solid oxide nitrogen oxide gas sensor of the present invention is a nitrogen oxide gas.
As such a nitrogen oxide gas, a known nitrogen oxide gas is measured without any particular limitation, but usually, a nitrogen monoxide gas, a nitrogen dioxide gas, and a mixed gas thereof are targeted.

The first aspect of the solid oxide nitrogen oxide gas sensor proposed by the present invention is that the solid electrolyte layer has a detection electrode layer containing an electron conductive material and a metal nitrate and / or a metal nitrite on the surface thereof, A counter electrode layer including a conductive material and having a surface covered with a coating material is formed, and a potential variable device and an ammeter are provided between the detection electrode layer and the counter electrode layer. The gas sensor is called a bipolar gas sensor).

In a second embodiment, a detection electrode layer containing an electron conductive material and a metal nitrate and / or a metal nitrite is formed on the surface of the solid electrolyte layer, and the surface is coated with a coating material containing the electron conductive material. And a reference electrode layer containing an electron conductive material is formed, a potential variable device is provided between the detection electrode layer, the counter electrode layer and the reference electrode layer, and between the detection electrode layer and the reference electrode layer. (Hereinafter, the gas sensor of this embodiment is referred to as a three-pole gas sensor).

In any of the solid electrolyte type nitrogen oxide gas sensors, the detection electrode layer in contact with the gas to be measured contains metal nitrate and / or metal nitrite, and the counter electrode layer paired with the metal nitrate and / or metal nitrate is formed of a coating material. A major feature is that the surface is covered. And in the bipolar gas sensor,
Each potential variable device is provided between the detection electrode layer and the counter electrode layer, and in the case of a three-electrode gas sensor, between the detection electrode layer, the counter electrode layer, and the reference electrode layer, and in the former, the detection electrode layer and the counter electrode layer are provided. By applying a voltage to the detection electrode layer directly with respect to the reference electrode layer, or in the latter case, the detection electrode layer can be controlled to have a positive potential higher than that of the counter electrode layer. In any of the aspects of the gas sensor, an ammeter is provided between the detection electrode layer and the counter electrode layer, and the current flowing between the two electrodes when the detection electrode layer is applied to a more positive potential than the counter electrode layer. It has a structure that can measure the value.

According to the gas sensor having such a structure, when the detection electrode layer is applied at a more positive potential than the counter electrode layer in the gas to be measured as described above, the metal nitrate and / or metal nitrite contained in the detection electrode layer Dissociates to form metal ions,
Since this moves from the detection electrode layer toward the counter electrode layer, the concentration of nitrogen oxides contained in the gas to be measured can be measured according to the principle assumed as follows.

For example, if the nitrogen oxide gas contained in the gas to be measured is nitrogen dioxide gas and the detection electrode layer contains lithium nitrate, LiNO ₃ = Li ⁺ + NO _{2 in the} detection electrode layer _{+ (1/2) O 2 + e} - lithium ion dissociation equilibrium reaction takes place, that is the dissociation of the
It moves to the counter electrode layer at a lower potential than the detection electrode layer. Then, since the counter electrode layer is covered with the covering material,
The lithium ions that have moved to the counter electrode layer are stabilized without involving nitrogen oxides in the gas to be measured. As a result, a current flows from the sensing electrode layer to the counter electrode layer between the sensing electrode layer and the counter electrode layer. This current value correlates when the nitrogen oxide concentration in the gas to be measured changes because it affects the dissociation equilibrium reaction in the detection electrode layer.

For example, when the nitrogen oxide is not contained in the gas to be measured, the reaction proceeds in the direction in which the metal nitrate dissociates. In the parallel reaction, the equilibrium is inclined toward the generation of metal nitrate, and as a result, the value of the current flowing between the electrodes is reduced. As the nitrogen oxide concentration in the gas to be measured increases, the value of the current flowing between the electrodes further decreases. Therefore, in the gas sensor of the present invention, the current value flowing between the sensing electrode layer and the counter electrode layer is measured by an ammeter provided between these two electrodes, and the current value prepared in advance and the nitrogen oxide gas are measured. By associating with a calibration curve showing a correlation with the concentration, the concentration of the nitrogen oxide gas in the gas to be measured can be known.

According to the gas sensor capable of measuring the concentration of nitrogen oxide gas in the gas to be measured in this manner, alkali ions consumed by the dissociation equilibrium reaction of the alkali metal nitrate contain only a small amount of nitrogen oxide in the gas to be measured. However, if it is present, the dissociation equilibrium reaction has a large inclination in the direction in which metal nitrate is generated, so that the alkali metal nitrate and / or alkali metal nitrite, as in a conventional current detection type solid electrolyte gas sensor, is used. Consumption does not progress unilaterally.

For this reason, the consumption of the metal nitrate and / or metal nitrite contained in the detection electrode layer gradually progresses, and the gas sensor can stably measure the nitrogen oxide gas concentration for a long period of time. Further, since a slight change in the nitrogen oxide gas concentration appears as a current change, the measurement in a low concentration region is more accurate than that of a conventional solid oxide nitrogen oxide gas sensor of the electromotive force detection method.

The gas sensor of the present invention having the above structure is
And the solid electrolyte layer contains a known solid electrolyte.
Adopted without restrictions. For example, NASICON (Na_{1 + A}Zr_TwoSi_AP_3-A
O₁₂Where 0 ≦ A ≦ 3), β-Al_TwoO_ThreeNa-based ion transmission
Conductor or Li_TwoTiSiO_Five, Li_TwoSi_TwoO _Five, Li_FourSiO_Four, And LiLa₉(Si
O_Four)₆O_TwoCation conductors such as Li-based ion conductors
No.

The solid electrolyte layer may further contain ceramics such as silica, zirconia, titania and alumina for the purpose of improving moisture resistance and moldability in addition to the solid electrolyte. Known materials can be used for these ceramics without limitation, but oxides are preferable because of their excellent moisture resistance, and zirconia, titania, zirconium silicate, and the like are particularly preferable.

Although the content of the solid electrolyte in the solid electrolyte layer is not particularly limited, the total weight of the solid electrolyte layer is 100% by weight.
It is preferably 40 to 100% by weight, particularly preferably 60 to 100% by weight.

As a method for forming the solid electrolyte layer, a known method is employed without any particular limitation. As a typical forming method,
A method of baking the solid electrolyte synthetic material, heating after molding, a method of molding and then sintering the solid electrolyte synthetic material, and kneading the solid electrolyte synthetic material with a solvent and a binder to form a paste, A method in which the paste is printed on a ceramic or glass substrate by a screen printing method or the like and baked is used.

Although the thickness of the solid electrolyte layer is not particularly limited, it is generally adopted in the range of 0.02 mm to 2.0 mm.

The sensing electrode layer provided on the surface of the solid electrolyte layer is a portion that directly contacts the gas to be measured and is open to the atmosphere. The electron conductive material is a substance necessary for current detection and voltage application of the sensor, similar to the electron conductive material contained in the counter electrode layer or the reference electrode layer described below,
Known materials are used without limitation. For example, platinum, gold,
Noble metal elements such as palladium and silver and their alloys,
Alternatively, a mixture of two or more of the above-mentioned noble metal elements is employed, but platinum, gold, and mixtures or alloys thereof are particularly preferable because of their excellent corrosion resistance.

The content of the electron conductive material in the sensing electrode layer is not particularly limited, but is preferably 5 to 95% by weight based on 100% by weight of the total weight of the sensing electrode layer.
Particularly, it is preferably from 10 to 90% by weight.

The metal nitrate and / or metal nitrite contained in the sensing electrode layer is a substance capable of dissociating metal ions in an atmosphere containing a nitrogen oxide gas and generating a current by applying a voltage. Known ones are used without limitation, but alkali metal nitrates and mixtures thereof, or alkali metal nitrites and mixtures thereof are preferable because they easily dissociate metal ions.For example, sodium nitrate, lithium nitrate, potassium nitrate, nitric acid Examples thereof include alkali metal nitrates such as rubidium and the like, and alkali metal nitrites such as sodium nitrite, lithium nitrite, potassium nitrite and rubidium nitrite. Particularly, it is preferable to use lithium nitrate, sodium nitrate and a mixture thereof. If these metal nitrates and metal nitrites are not contained in the detection electrode layer, metal ions cannot be dissociated in the gas to be measured containing nitrogen oxide gas, so that the nitrogen in the gas to be measured cannot be dissociated. Since no current corresponding to the oxide gas concentration is generated, the measurement of the nitrogen oxide gas concentration becomes impossible.

The content of the metal nitrate and / or metal nitrite in the sensing electrode layer is not particularly limited, but is preferably 5 to 95% by weight based on 100% by weight of the total weight of the sensing electrode layer. In particular, it is preferably from 10 to 90% by weight in order to reduce the fluctuation of the current value of the sensor element during continuous use.

The structure of the sensing electrode layer is not particularly limited. A typical structure is, for example, a structure in which an electron conductive material and a metal nitrate and / or a metal nitrite are layered on the surface of the solid electrolyte layer. A structure in which metal nitrate and / or metal nitrite is dispersed in the electron conductive material of the sensing electrode layer, and a part or all of the metal nitrate and / or metal nitrite formed on the surface of the solid electrolyte layer A structure coated with a substance is exemplified. In particular, a structure in which the metal nitrate and / or the metal nitrite is dispersed in the electron conductive material is preferable because the detection electrode layer can be easily formed.

As a method for forming the sensing electrode layer, a known method is used without any particular limitation. For example, a method in which the above-mentioned electron conductive material and metal nitrate and / or metal nitrite are used alone or mixed, then kneaded with a solvent and a binder to form a paste, and the paste is baked on the surface of a solid electrolyte layer by a screen printing method or the like. In addition, a method in which an electron conductive material and a metal nitrate and / or a metal nitrite are formed by a thin film forming technique such as sputtering or vapor deposition is preferably employed.

The thickness of the sensing electrode layer is not particularly limited, but is generally adopted in the range of 0.001 to 0.03 mm.

In the gas sensor of the present invention, the surface of the counter electrode layer is coated with a coating material. If the surface is not coated, the counter electrode layer will come into direct contact with the gas to be measured,
Metal ions contained in the solid electrolyte react with the nitrogen oxide gas in the gas to be measured, and metal nitrate and / or metal nitrite are formed in the counter electrode layer. When such a reaction occurs, the dissociation equilibrium reaction in the sensing electrode layer in the sensing electrode layer is inhibited, and metal nitrate and / or metal nitrite are continuously consumed, so that long-term stability cannot be maintained.

In the present invention, the coating material for coating the counter electrode layer is preferably formed of an inorganic oxide, or has a property of being impermeable to nitrogen oxide and permeable to oxygen from the atmosphere. If the counter electrode layer is covered with such a coating material, in the pair pole layer, the following equilibrium reaction Li ⁺ + (1/2) migrated to have metal ions (as described in Li-ion) are involved O ₂ + e ^- = LiO ₂ is generated stably. Here, as the inorganic oxide, for example, a cement, a crystalline oxide such as an inorganic adhesive or a glass, an amorphous oxide such as a thin film, or the like is employed. In particular, glass is excellent in moldability. This is preferable.

As a method of coating the above-mentioned counter electrode layer with a coating material, a known method is used without any particular limitation. For example, a method of applying and drying the paste of the inorganic oxide on the counter electrode layer, a method of covering the counter electrode layer with a coating material thin film by a sputtering method, and the like are employed. The thickness of the coating layer is not particularly limited, but is generally adopted in the range of 0.005 to 0.1 mm.

The requirements for the electron conductive material for forming the counter electrode layer, the forming method, the thickness, and the like are the same as those of the above-described detection electrode layer.

In the present invention, in the three-electrode gas sensor, a reference electrode layer is provided on the surface of the solid electrolyte layer together with the detection electrode layer and the counter electrode layer. Here, the reference electrode layer is an electrode used as a reference for potential control when the detection electrode layer is set to a more positive potential than the counter electrode layer. By providing the reference electrode, the potential of the detection electrode can be further stabilized. it can.

In the present invention, it is more preferable that the surface of the reference electrode is covered with a covering material from the viewpoint of stabilizing the potential. As such a coating material, a material made of an inorganic oxide as described in the counter electrode layer is preferable.

The requirements for the electron conductive material for forming the counter electrode layer, the forming method, the thickness, and the like are the same as in the case of the detection electrode layer described above.

In the present invention, the arrangement of the detection electrode layer, the counter electrode layer, and the reference electrode layer provided in the triode-type gas sensor is not particularly limited as long as each is in contact with the solid electrolyte layer. Generally, a sensing electrode layer is provided on one surface of the solid electrolyte layer, and a counter electrode layer and a reference electrode layer are provided at a certain distance on the other surface, but all the electrode layers are formed of the solid electrolyte layer. It may be provided at a fixed distance on the same surface.

In the present invention, when the nitrogen oxide gas concentration is measured, in the bipolar gas sensor, the detection electrode layer has a higher potential than the counter electrode layer between the detection electrode layer and the counter electrode layer. And a voltage is applied between the detection electrode layer and the reference electrode layer so that the detection electrode layer has a more positive potential than the reference electrode layer. In order to perform stable measurement with higher sensitivity, it is necessary to apply a voltage to the detection electrode layer so as to be 30 to 200 mV to the counter electrode layer or the reference electrode layer, preferably to about 50 to 100 mV. preferable.

In the present invention, both the bipolar gas sensor and the triode gas sensor can be operated at room temperature. However, in order to stably measure the nitrogen oxide concentration, a known solid electrolyte type gas sensor is used. As with the carbon dioxide sensor, 50
It is preferable to use by heating to a constant temperature of from ℃ to 600 ℃. As a method of heating the gas sensor, heating from a heat source external to the gas sensor may be used, or a solid electrolyte or ceramic substrate having a heater may be joined to the gas sensor and heated by applying a DC or AC voltage to the heater. May be. The mounting position of the heater to be joined to the gas sensor is not particularly limited as long as it does not hinder the operation of the gas sensor, such as on the counter electrode layer or the reference electrode layer.

[0047]

The solid oxide nitrogen oxide gas sensor of the present invention exhibits high sensitivity even in a low-concentration atmosphere, and can stably measure the nitrogen oxide gas concentration for a long period of time. Therefore, the present invention has great technical significance in that nitrogen oxide gas can be measured accurately over a long period of time.

[0048]

EXAMPLES The present invention will be described specifically with reference to the following examples, but the present invention is not limited to these examples.

Example 1 A three-electrode sensor having the structure shown in FIG. 1 was manufactured as a current detection type solid electrolyte type nitrogen oxide gas sensor.
That is, in this solid electrolyte type nitrogen oxide gas sensor, the detection electrode layer 1 was formed on one surface of the solid electrolyte layer 4, and the counter electrode layer 2 and the reference electrode layer 3 were formed on the other surface. The upper and both side surfaces of the counter electrode layer 2 and the reference electrode layer 3 were covered with the glass 4. A potential variable device 6 is provided between the detection electrode layer 1, the counter electrode layer 2 and the reference electrode layer 3, and an ammeter 7 is provided between the counter electrode layer 2 and the detection electrode layer 1. there were.

In the solid oxide nitrogen oxide gas sensor having such a structure, the solid electrolyte layer 3 was formed by the following method. LiOCH ₃ , as a solid electrolyte,
_{Ti (O-n-C 4} H 9) 4, Si (OC 2 H 6) 4, and Z
_{r (O-n-C 4} H 9) 2 to ₄ of the metal alkoxide in a molar ratio: 1: 2: After reacting at 1, by firing 4 hours in an air atmosphere of 750 ° C., 50 mol% Li ₂
A powder of TiSiO ₅ +50 mol% ZrSiO ₄ was obtained.
After uniaxially molding this solid electrolyte powder, it is baked in an air atmosphere at 500 ° C. for 2 hours and then sintered in an air atmosphere at 1200 ° C. for 6 hours to have a diameter of 4.0 mm and a thickness of 0.5 mm. This was used as a solid electrolyte layer 3 as a disk-shaped pellet.

The detection electrode layer 1 was prepared by kneading a commercially available gold paste and lithium nitrate at a ratio of 25% by weight with respect to the gold paste, and printing and drying on one surface of the solid electrolyte layer 3.
It was baked for 1 hour in the air at 0 ° C. to form a thickness of 0.015 mm.

Similarly to the detection electrode layer, the counter electrode layer 2 and the reference electrode layer 3 were prepared by printing, drying, and drying a commercially available gold paste on the surface of the solid electrolyte layer 4 opposite to the surface on which the detection electrode layer 1 was formed. 65
Baking for 1 hour in the air at 0 ° C, 0.015m each
m.

The upper surface and both side surfaces of the counter electrode layer 2 and the reference electrode 3 are
A commercially available glass powder is added to terpineol in which 5% by weight of ethylcellulose is dissolved, and the mixture is covered with a glass paste obtained by adding and kneading the same amount of terpineol with respect to the weight of terpineol. And coated. The thickness of the coated glass was 0.015 mm.

The current detection type solid electrolyte type nitrogen oxide gas sensor manufactured by the above method is placed in an electric furnace in which the concentration of nitrogen dioxide gas can be freely controlled.
Heated to 50 ° C. With the temperature of the sensor kept at 150 ° C., the detection electrode layer potential was set to 100 mV with respect to the reference electrode layer potential.
And the nitrogen dioxide gas concentration in the electric furnace is set to 0 ppb, 500 ppb, and 100 ppb.
0 ppb was set. At this time, the value of the current flowing between the detection electrode layer and the counter electrode layer was measured by the ammeter 7 for each concentration.

Such a measurement was carried out immediately after the production of the sensor, one week later, and one month later. The results are shown in Table 1. In each case, the nitrogen dioxide gas concentration was 500 ppb, 0 ppb, and 1000 ppb.
The difference between the current value at the time of pb and the current value at the time of 0 ppb was determined, and this was defined as sensitivity (500) and sensitivity (1000), respectively. In addition, the sensitivity after one month from the initial sensitivity (1000) (100
0) was determined by the following equation, and evaluated as a sensitivity change rate.

(Sensitivity after one month (1000)) / (initial sensitivity (1000)) × 100 (%) The results obtained are shown in Table 2. The sensitivity (1000) was almost double the sensitivity (500). That is, a sensitivity proportional to the concentration was obtained. Further, a stable sensitivity was obtained over time.

Example 2 A bipolar sensor having the structure shown in FIG. 2 was fabricated as a current detection type solid electrolyte type nitrogen oxide gas sensor.
That is, in this solid electrolyte type nitrogen oxide gas sensor, the detection electrode layer 1 is formed on one surface of the solid electrolyte layer 4 and the counter electrode layer 2 is formed on the opposite surface. The upper surface and both side surfaces of the counter electrode layer 2 are glass 5
Covered by A potential variable device 6 was provided between the counter electrode layer 2 and the detection electrode layer 1, and an ammeter 7 was provided between the counter electrode layer and the potential variable device.

In the solid electrolyte type nitrogen oxide gas sensor having such a structure, the solid electrolyte layer 4, the sensing electrode layer 1, the counter electrode layer 2, and the coating material covering the upper surface and both side surfaces of the counter electrode layer 2 are the same as those in the first embodiment. Example 1 using the composition and structure of
It was prepared in the same manner as described above.

The operation of the solid electrolyte type nitrogen oxide gas sensor of the current detection type produced by the above method is performed except that the detection electrode layer potential is controlled by the potential variable device 6 so as to be 100 mV with respect to the counter electrode layer potential. Performed in the same manner as in Example 1. The detected current values are shown in Table 1.

The sensitivity and the rate of change in sensitivity were evaluated in the same manner as in Example 1. These results are shown in Table 2. A sensitivity proportional to the concentration was obtained, and a stable sensitivity was obtained over time.

Comparative Example 1 A sensor having the structure shown in FIG. 3 was manufactured as the solid electrolyte type nitrogen oxide gas sensor of the current detecting method of Comparative Example 1. That is, in this solid electrolyte type nitrogen oxide gas sensor, the detection electrode layer 1 was formed on one surface of the solid electrolyte layer 4, and the counter electrode layer 2 and the reference electrode layer 3 were formed on the other surface. The upper surface and both side surfaces of the reference electrode layer 3 were covered with the glass 4. A potential variable device 6 is provided between the detection electrode layer 1, the counter electrode layer 2 and the reference electrode layer 3, and an ammeter 7 is provided between the counter electrode layer 2 and the detection electrode layer 1. there were.

In the solid electrolyte type nitrogen oxide gas sensor having such a structure, the solid electrolyte layer 4, the sensing electrode layer 1, the counter electrode layer 2, the reference electrode 3, and the coating material for covering the upper surface and both side surfaces of the reference electrode 3 are described in Examples. Using the same composition and structure as in 1,
It was produced in the same manner as in Example 1. Further, the second embodiment is the same as the first embodiment except that the potential variable device 10 controls the detection electrode layer potential to be -100 mV with respect to the reference electrode layer potential. The detected current values are shown in Table 1.

The sensitivity and the rate of change of sensitivity were evaluated in the same manner as in Example 1. These results are shown in Table 2. Although a sensitivity proportional to the concentration was obtained, the sensitivity greatly fluctuated with time, and stable sensitivity could not be obtained in a long-term measurement.

Comparative Example 2 A sensor having the structure shown in FIG. 4 was produced as a solid oxide nitrogen oxide gas sensor of the electromotive force detection system.
In this solid electrolyte type nitrogen oxide gas sensor, a detection electrode layer 1 is formed on one surface of a solid electrolyte layer 4 and a counter electrode layer 2 is formed on the opposite surface. The upper surface and both side surfaces of the counter electrode layer 2 are covered with glass 5. Further, a voltmeter 8 was provided between the counter electrode layer 2 and the detection electrode layer 1.

The solid electrolyte type nitrogen oxide gas sensor of the current detection type produced by the above method was placed in an electric furnace in which the concentration of nitrogen dioxide gas could be freely controlled, and the sensor was replaced with one.
Heated to 50 ° C. With the temperature of the sensor kept at 150 ° C. and the temperature of the sensor element kept at 150 ° C., the nitrogen dioxide gas concentration in the electric furnace was set to 0 ppb and 500 pp.
b and 1000 ppb, and the electromotive force generated between the sensing electrode layer and the counter electrode layer was measured at each concentration. The difference in electromotive force between when the nitrogen dioxide gas concentration was 500 ppb and when the nitrogen dioxide gas concentration was 1000 ppb was determined, and this was used as the sensitivity.

Table 3 shows the results. The electromotive force was substantially the same when the nitrogen dioxide gas concentration was 500 ppb and when the nitrogen dioxide gas concentration was 1000 ppb, and no sensitivity was obtained.

[0067]

[Table 1]

[0068]

[Table 2]

[0069]

[Table 3]

[0070]

[Brief description of the drawings]

FIG. 1 is a sectional view showing a typical embodiment of a three-electrode type solid electrolyte type nitrogen oxide gas sensor based on a current detection method used in the present invention.

FIG. 2 is a cross-sectional view showing a typical embodiment of a bipolar type solid electrolyte type nitrogen oxide gas sensor using a current detection method used in the present invention.

FIG. 3 is a cross-sectional view showing a typical mode of a three-electrode type solid electrolyte type nitrogen oxide gas sensor using a conventional current detection method.

FIG. 4 is a cross-sectional view showing a typical mode of a nitrogen oxide gas sensor using an electromotive force detection method.

[Explanation of symbols]

 1. Detection electrode layer 2. Counter electrode layer 3. Reference pole layer 4. Solid electrolyte 5. Glass 6. Potential variable device 7. Ammeter 8. voltmeter

Claims (4)

[Claims] 1. A detection electrode layer containing an electron conductive material and a metal nitrate and / or a metal nitrite, and a counter electrode layer having a surface covered with a coating material containing an electron conductive material are formed on a surface of a solid electrolyte layer. A solid electrolyte type nitrogen oxide gas sensor characterized in that a potential variable device and an ammeter are provided between the detection electrode layer and the counter electrode layer. 2. A solid oxide nitrogen oxide gas sensor according to claim 1, wherein a voltage is applied between said detection electrode layer and said counter electrode layer such that said detection electrode layer has a more positive potential than said counter electrode layer. ,
A method for measuring a nitrogen oxide gas concentration, comprising measuring a current value flowing between both electrode layers and measuring a nitrogen oxide gas concentration in a gas to be measured. 3. A detection electrode layer containing an electron conductive substance and a metal nitrate and / or a metal nitrite on the surface of a solid electrolyte layer, a counter electrode layer comprising an electron conductive substance and a surface coated with a coating material, and an electron. A reference electrode layer containing a conductive material is formed, a potential variable device is provided between the detection electrode layer, the counter electrode layer and the reference electrode layer, and an ammeter is provided between the detection electrode layer and the counter electrode layer. A solid electrolyte type nitrogen oxide gas sensor characterized by comprising: 4. A solid electrolyte type nitrogen oxide gas sensor according to claim 3, wherein a voltage is applied between the detection electrode layer and the reference electrode layer such that the detection electrode layer has a more positive potential than the reference electrode layer. A method for measuring a nitrogen oxide gas concentration, comprising: measuring a current value applied and flowing between a detection electrode layer and a counter electrode layer to measure a nitrogen oxide gas concentration in a gas to be measured.